1. Field of the Invention
This invention relates to apparatus for use in the chemical analysis of biological fluids and, more particularly, to apparatus for automated metering of biological fluids onto test elements.
2. Description Relative to the Prior Art
A number of automated systems have been developed for performing quantitative chemical analysis of biological fluids, such as blood serum. Most of the commercially available systems utilize liquid reagents and require analyzer equipment having complex solution handling and transport capabilities. Recent developments, however, have provided test elements for biological fluid analyzers in essentially planar, dry form. One form of such a test element is disclosed in U.S. Pat. No. 4,053,381 to Hamblin, et al granted on Oct. 11, 1977. This patent describes a test element of the type which comprises a pair of electrodes, selective to the ion activity of choice, supported on a substrate and having a generally planar strip form, and a bridge used to promote ionic migration between a reference fluid and a patient sample fluid. The electrical signal derived from the pair of electrodes is indicative of the test ion activity and thus of the ion concentration. Another form of test element is disclosed in commonly-owned U.S. Pat. No. 3,992,158 to Przybylowicz, et al granted on Nov. 16, 1976. The test element disclosed in this patent is formed as a multi-layered element containing the necessary reagents for reaction with components of a biological fluid deposited thereon. Certain reactions colorimetrically produce a change in optical density in the element which is sensed by a reflectometer, the amount of light reflected from the element varying in accordance with the reaction and being indicative of the amount of a particular analyte present in the fluid.
In performing the chemical analysis of biological fluids such as blood serum, it is frequently desirable to process samples of such fluids on test elements of both the potentiometric and colorimetric types. The former requires the metering of small precise amount of reference fluid and patient sample fluid onto the test element whereas the latter requires only the metering of the patient sample fluid. An analyzer adapted to process both potentiometric and colorimetric test elements is disclosed in the aforementioned commonly-assigned U.S. pat. application Ser. No. 159,564, now U.S. pat. No. 4,296,070. In order to manufacture such a dual capability analyzer at a commercially acceptable cost and size, the individual analyzer components must be compact, efficient, and able to function in close proximity with other components. More specifically, a reference fluid metering device must be provided for use in conjunction with the patient sample fluid metering device for depositing a predetermined quantity of reference fluid onto a potentiometric test element supported in a metering station of the analyzer. The potentiometric test elements used in the analyzer have exterior dimensions of approximately 2.5 mm by 3.0 mm and require the reference fluid metering device to deposit the reference fluid onto the test element at a position spaced only approximately 1 mm from the patient sample fluid concurrently deposited on the test element by the sample fluid metering device.